Tungsten alloy



Patented June 17, 1952 THNGSTEN ALLOY No Drawing. Application ctdber,30, 1945;' SerialNo. 625,691;

7 Claim.

The'present inventionrelates :to *sinteredzalloys of tungsten drgnou machinability; high density afid fiarunessi Tungsten is well known to be a very refractory the a sense that it :1 has a melting: point oi about 3400 C. Suchia refractoryi-metallmay be workedfi in the most economical manner by powder: metallurgy methods,:. and such. methods are generally: employed in producing this metal for commercial iuses; Thetungstentpowder isiirst shaped into ingotlform insv a mold? under: high pressure: It is then:- presintered in an hydrogen atmosphere at altemperatureeof, 1000 C. so that the ingot canrthen be handled; The ,next step, accordingly; is toplace'ztliefingot in anzelectric circuit; also in a hydrogen? atmosphere, andpass aficurrent through' it equivalent toaboutt 90;%-. of its -fusinge'temperature; or about" 2900' 0;, thus finally sintering it.

Atttiis stage of working, the: tungsteningot is very'strong). rather brittle-and quiteahard. Its density, however; must be further increased, and other: desirable qualities; must be givena'it; This effected: by swaging the ingot-underheat; The rod so formed:- has at theoreticalidensity: of about 19.3 grams per" cubic centimeter; and may-be drawni down: to very? finer wires of a tensile s'treiig-th far: surpassing that'of; steelpiano wire of; equal diameter.

Intm'anyf'other'respects; however; the purehot swageditungst'en metalleaves much to bedesired. lt isfverly'hard'to machine; for instance, and con.- sequently only the simplest shapes can be made fro'mkit, eitherby cutting off sections of a rod of circular cross-section, or by punching circular pellets from a flat sheeitbothof which methods ,have been used in making electrical contact points for automobiles.

The uses of this very desirable metal can be increased-tea very. greatextent' ii'it can be made amenable to a greater degree of working, that would make it possible to form it into shapes having,- a wider field of usefulness withoutgreatly impairing its inherent natural qualities.

In application for patent of Kurtz and Williams; Serial No. 460,226,. now Patent No. 2,4911866, issued December 20, 1949 there is disclosed an alloy consisting mainly of tungsten but having alloyed therewith small quantities of grain refining metalsuch as vanadium, and alloying, bonding and densifying metals such as manganese, iron, cobalt and nickel, and metal of the platinum family, and goldv Thismetal by sintering without swaging can be made with a density as high as or higher than: that of pure hot swaged a.

cles, and which, while it has somewhat less density; metal; disclosed; in the; Kyrtz; and Williamsa applications, nevertheless has; a. very hielrdensitys-without a in s 1. 1. it er and has g0 odimachinability. It: may also be; molded into a wide variety of shapes such; a rl 9ibl disks; plates and;,,in facti n ef m to any: specifications,..

It is a further object .toproducean alloy that is .basicallytungsten, that possesses in large part thedesirablepropertiesof pure. hot swagedtungsten, but which is capable of machining andshap; ing;toa: degree; that is impossible; with pure hot swaged tungsten. The a-lloy of thepresentinvention: is; sintered at; temperatures; no higher than the range of rapid; germination tempera;- tures; but; is; comparablev withpure hot swaged tungsten-V in; density and superior, to. it in ma,- chi abi i y, a a y th anro ertiea It has; prev ou y e o n d ou ha h range of 1300-1800 C., rapid ,crystalliaation of tungsten takes place. and it isaat; these temperatunes; that the presentalloy is sintered fora period sufiicient -.to;produce-alarge number -oi fine; crystals; It is; proposed, incthe method ofthe present invention not to exceed thesetemperatures greatly;

I have found that; in; powder metallurgy methods as; applied to tungsten, the; coherence and fineness of grain can-be; considerably promoted byfadding to the basic tungsten metal powders certain other powdered metalshaving melting pointswithinor-slightly below the-rapidcrystallir zat-ion range of;the tungsten metal ashereinabove defined;

The metals to be added to the refractory metals are cobalt. and: platinum. and coppe or; silver or both.

The addition of' cobalt increases the density and fineness: of; grain at; temperatureswithin the range stated, but; the addition of cobalt alone gives; an extreme; hardness to the ultimate alloy hat ma es i dif cul '0 ma i Platinum, as an addition to the tungsten metal, has much the same effect as cobalt, in increasing densitythough-v not. hardness. However, theJcoI- balt; andv the platinum: may be so combined as additions te the tungsten as to give high density. sufllcient hardness for the; desired purpose, and goodmachinability. The addition of cobalt and platinum should; bevery small. for the besteffects. Eon instance, an addition of 5%, cobalt Q even ch le s, rod ce lo o very' hi h density, about 17.7 grams; per cubic; centimetres iff0 .5% platinum be added. Withso much cobalt, however, the resultant alloy is-veryhard and, while machinable, is very diflicult to machine. It has 3.6 l zardness on the Rockwell A scale of about Within the ambit of this invention it is, in-

te ded. t inc u e. n ll y o u stea, witho balt also, in an amount not exceeding and a platinum group metal in an amount not exceeding 1% and an amount of silver and copper not exceeding combined.

As examples of such alloys, the following will serve:

The proportions given are by weight.

Alloy A has a density of 17.2. It has good machinability and a hardness on the Rockwell A scale of about 63. It is a metal suited for contact points and other uses, such as electrodes of any desired shape.

Alloy B has a density of 16.7. It has considerable hardness due to the somewhat large cobalt addition, but is machined easily.

Alloy C has a density of 17.8, a hardness on the Rockwell A scale of about 63, and good machinability.

The additions of copper and silver in combination with cobalt and platinum promote the densifying action and I find them to be beneficial in increasing the conductivity of the alloy and improving the machinability. The alloys of the invention may contain for best results from 84%- 90% tungsten, from 1%-5% cobalt, from 1%- 10% of copper-silver or both combined, and from 0.1 %-1.0% of platinum.

The platinum may be added as powder but is so small in amount that it preferably should be added to the powdered metals as a solution of a water-soluble compound, such as chlorplatinic acid, in order to secure even distribution.

The powdered metals are impregnated with the chlorplatinic acid solution and dried in the .air. They are then pressed in a mold and heated in a non-oxidizing atmosphere at a temperature of 1300 C. to 1800 C. for from one to three hours.

After this heat treatment the metal shows a remarkable grain growth. The grain count shows not less than 2000 grains per square millimeter and may be as high as 20,000 grains per square millimeter.

The metals added to the tungsten have in each case a melting point within or below the temperature of rapid crystallization of the tungsten, namely, 1300 C. to 1800 C. Under the heat treatment given, a homogeneous alloy is formed with a minimum of voids and a density in the neighborhood of 17, a hardness of about 63 on the Rockwell A scale and good machinability. In general it may be stated that with the increase of the amount of cobalt, there is an increase in hardness, a property which is desirable in many instances, but if the addition of cobalt be too great, that is, much beyond 5%, the hardness increases to such an extent that machining is difficult if not impossible. The alloy formed from the constitutents given is a homogeneous alloy characterized by very fine grain structure and a grain count of not less than 2,000 grains per square millimeter. If desired, after the sintering is completed, the sintered body may be subjected to a coining operation either at room temperature or at elevated temperatures.

Having thus described my invention, what I claim is:

1. A dense coherent tungsten alloy consisting 4 of 84% tungsten, 5% cobalt, 5% copper, 5% silver and 1% platinum, having a density of 16.7 grams per cubic centimeter and a grain count of not less than 2,000 grains per square millimeter and good machinability.

2. A dense coherent tungsten alloy consisting of 89.9% tungsten, 1% cobalt, 5% copper, 4% silver and 0.1% platinum, having a density of 17.2 grams per cubic centimeter and a rain count of not less than 2,000 grains per square millimeter and good machinability.

3. A dense coherent tungsten alloy consisting of 84% tungsten, 5% copper and 5% silver to which has been added as an addition cobalt and platinum in the relation of 5% cobalt to 1% platinum, having a density of 16.7 grams per cubic centimeter and a grain count of not less than 2000 grains per square millimeter and good machinability.

4. A dense coherent tungsten alloy consisting of 89.9% tungsten, 5% copper and 4% silver, and an addition of cobalt and platinum in the proportion of 1% cobalt to 0.1% platinum, having a density of 17.2 grams per cubic centimeter and a grain count of not less than 2000 grains per square millimeter and good machinability.

5. A dense coherent tungsten alloy consisting of tungsten, 4% copper and 3% silver and having an addition of cobalt and platinum in the proportion of 2% cobalt to 1% platinum, said alloy having a density of 17.8 grams per'cubic centimeter and a grain count of not less than 2000 grains per square millimeter and good ma.- chinability.

6. A dense coherent tungsten alloy consisting of 84% to 90% tungsten, 3% to 5% silver, 4% to 5% copper, 1% to 5% cobalt and .1 to 1% platinum, the alloy so formed having a density approximating 17 grams per cubic centimeter and a grain count of not less than 2000 grains per square millimeter and good machinability.

7. A dense coherent tungsten alloy consisting of 84% to 90% tungsten, 1% to 10% copper-silver, 1% to 5% cobalt and .1 to 1% of platinum, the alloy so formed having a density approximating 17 grams per cubic centimeter and a grain count of not less than 2000 grains per square millimeter and good machinability.

JACOB KURTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,167,827 Kaiser Jan. 11, 1916 1,346,192 Gebauer July 13, 1920 1,447,797 Adams Dec. 18, 1923 1,807,581 Bates June 2, 1931 1,822,682 Weiger Sept. 8, 1931 2,030,229 Schwarzkopf Feb. 11, 1936 2,072,368 Jedele Mar. 2, 1937 2,183,359 Smithells Dec. 12, 1939 2,370,242 Hensel et a1 Feb. 27, 1945 2,389,060 Kurtz Nov. 13, 1945 FOREIGN PATENTS Number Country Date 447,567 Great Britain May 21, 193 6 OTHER REFERENCES Hansen: Aufbau de Sweistofllegierungen, published by Edwards Brothers, AnnArbor, Michigan 1936, pages 606-609, 1025 and 1026. 

7. A DENSE COHERENT TUNGENT ALLOY CONSISTING OF 84% TO 90% TUNGENT, 1% TO 10% COPPER-SILVER, 1% TO 5% COBALT AND .1 TO 1% OF PLATINUM, THE ALLOY SO FORMED HAVING A DENSITY APPROXIMATING 17 GRAMS PER CUBIC CENTIMETER AND A GRAIN COUNT OF NOT LESS THAN 2000 GRAINS PER SQUARE MILLIMETER AND GOOD MACHINABILITY. 